This disclosure relates generally to x-ray generation systems, and more particularly to an x-ray tube target and a method of repairing a damaged x-ray tube target for x-ray generation.
X-ray tubes generally include a cathode assembly and an anode assembly disposed within at least one vacuum vessel or enclosure. The cathode assembly is positioned at some distance from the anode assembly, and a voltage difference is maintained therebetween in order to extract and accelerate electrons from the cathode assembly towards the anode assembly. This voltage differential generates an electric field gradient having a strength defined by the voltage differential between the anode assembly and cathode assembly divided by the distance therebetween. The anode assembly typically includes a rotating anode target having a target track that is generally fabricated from a refractory metal with a high atomic number, such as tungsten or a tungsten alloy. The rotating anode target is commonly a rotating disk configured so that the heat generated by the absorption of impinging electrons is spread out over a large circumferential area. The cathode assembly typically includes a cathode that emits electrons in the form of a focused electron beam that is accelerated across the voltage difference of a cathode to anode vacuum gap and produces x-rays upon impact with the track of the rotating anode target. Because of the high temperatures generated when the electron beam strikes the target track, it is necessary to rotate the anode target at a high rotational speed. As the electrons impact the target track, the kinetic energy of the electrons is converted to high-energy electromagnetic radiation, or x-rays. X-rays are emitted in all directions. A portion of the x-rays are directed out of the x-ray tube through an x-ray emission window in the x-ray tube housing. The x-rays are then transmitted through an object being imaged and intercepted by a detector that forms an image of the object's internal anatomy, contents or structure.
Newer generation x-ray tubes have increasing demands for providing higher peak power. Higher peak power results in higher peak temperatures occurring in the anode assembly, particularly at the target track. Thus, for increased peak power applied, there are endurance and reliability issues with respect to the anode target. Such effects may be countered to an extent by, for example, spinning the target faster. However, doing so has implications to reliability and performance of other components within the x-ray tube. As a result, there is a greater emphasis in finding materials and solutions for improved performance and higher reliability of anode target structures within an x-ray tube.
Over time, the target track of the anode target and possibly a portion of underlying substrate material may be damaged during use. Recovery rates of damaged anode targets are generally limited to targets with minimal track damage as candidates for reuse. Current methods for target reuse (refabrication and refurbishment) are track thinning and layer deposition. Track thinning includes machining away a portion of the x-ray target layer in attempt to remove the damaged material. This is only applicable to targets having damage limited to less than the full thickness of the focal track layer. Layer deposition includes machining away the x-ray target layer and replacing it with a deposited layer material. This is costly since it requires expensive deposition processes, such as plasma spray, chemical vapor deposition (CVD), physical vapor deposition (PVD), lazer engineered net shape (LENS), or electroplating (plating).
Therefore, there is a need for a method for repairing a damaged x-ray tube anode target that avoids the high costs associated with repairing a damaged anode target by layer deposition methods to achieve x-ray target reuse and enables significant savings in comparison to fabricating new x-ray tube anode targets.